Drill machine control apparatus



Filed Oct. 7, 1938 3 Sheets-Sheet 2 TOR INVEN fur ,L-MJ, flu MM;

A TTORNE Y3 Patented Feb. 13, 1940 UNITED STATES PATENT/OFFICE This invention relates to improvements in drill machine control apparatus ,1 v v More particularly, the invention pertains to improved control apparatus of this kind by which a a drill'while continuously rotating maybe re 'peatedly withdrawn and reinserted after succese sive increments of a deep drilling operation.

One of the mairn objectsof the invention is the provision in control apparatus of. this kind of improved, mechanism for automatically so controlling a drill as to cause it to rapidly move throughout an initial distance toward a piece of work at a. fast rate until it is in position to commence drilling thereon, to move into. thework to 16 a predetermined depth at a relatively slower rate,

to move away from the work at arapid rate inorder toolean the partially formed bore and cool the drill, and to return toward the work at said first mentionedfast rate throughout a distance equal to said initial distance plus the previous drilled depth. v

Another object of the invention is the provision of improved control mechanism of this kind-which comprises structurally sturdy parts that are not susceptible to breakage, to provide control mechanism of this kind which acts upon the valve: of a fluid pressure drill actuating system to cause the latter toperformtheforegoing cycle automatically until a bore of predetermined depth has been drilled; and to provide means for .adjustably predetermining the depth of each drilling step of a drilling operation by whichonly a single adjustment is required to drilling depth 015 each step at the same valve:

An illustrative embodiment of the invention is shown in the accompanying drawings, in which:

Fig. 1 is a fragmentary side elevational view of a drilLpress including control apparatus em-' bodying the invention. i Fig. 2 is a diagrammatic illustrations] view of the control apparatus shown in Fig. 1.

Fig. 3. is an enlarged transverse sectional :view

taken on the line 3--3 of Fig.1.

Fig. 4 is a side elevational view showing a pore, tion of the apparatus shown in Fig. 3, partially in sectionand partially in side elevation, as viewed from the line 44 of Fig. 3.

' Fig. 5 is a side elevational view of the apparatus shown in section in Fig. 3 as viewed from the line 5-5 of the latter flgure.- A

Fig. 6 is a fragmentarylongitudlnalsectional view taken onthe line 6-6 of Fig. 3.

Fig.7 is a fragmentary transverse sectional view taken on the line 'L-l of Flg'. 5.

Y Fig. 8 is a fragmentary transverse sectional view taken on the line fl 8 .oi Fig. 4.. 1

In the drawings is illustrated an embodiment" of the control, apparatus in ,a drill press comprising a basestructure ll on which 'is slidably 5 mounted a fixture I I in'whichis supported aroi tatable spindle I2 having a drill chuck IS. on its lower end. A drill ll engaged in the chuck i3 is adapted to perform a deep bore-drilling operation upona crankshaft l 5, or other piece ot work, l0 sultable mounted in a work support I6 carried by the base structure ID of the machine. ,cThe' drill spindle I2 has a splined upper end. portion l9 which is slidably but.non-rotatablyconnected with transmission gearing; 41 which is adapted to 15 be drivingly operated by 'amotor 18 having a pinion 20 meshed with the transmission, gearing IT. The transmission mechanism and motor are fixed with respect to the base-structure ID of the.

machine and the spindle I2 is adapted to slide in 20 the direction of its longitudinal axis with respect thereto. I I p The drilLH'is advanced toward and retracted from the work by movement of the fixture H relative to the base of the machine under the action 25 of the control'apparatus'embodying the .inven tion Thiscontrol apparatus includes. a fluid pressure system, diagrammatically shown in Fig, 2 which is mainly of conventional construction andwhich. is adapted to automatically rapidlysd advance the drill toward the work until it engages the latter, to slowly move the drill into the work during a limited drill operation comprisingonly an increment of thetotal depth of the bore being made. The apparatusthereafter rapidly 35 retracts the drill to facilitateacleaning oi the partially formed bore and cooling of the drill.- Thereafter the drillis rapidly advancedwagain toward the work throughout a distance including.

the partially formed depth of the bore". Each 5 successive retraction and advancement cycle-oi the drillthereiore necessitates the movement of 1 the drill throughoutan additional distance equal to the depth of the, previouslytformed increment H oi. thehore; The present inventionernbodies im- 45 provements of resetting. mechanism by which the g I increase in the length -oi rapid return movement of the drill is made aiter each successive partial drilling operation and subsequent withdrawal of.

the drill; .In order toclearlydescribe these imso provements, it is deemed necessary to describe thoperationoi' thefiuid pressure systemportion oi the apparatus. V i The fluidpressure system portion of. the: ap

paratusconiprises a reservoir having an outlet ll 22 connected with a pump 23 by which fluid medium is placed under pressure and supplied through a conduit 24 to a valve mechanism comprising a cylinder 25. Interposed between the valve mechanism 25 and the pump 23 is an accumulator 26 by which the fluid pressure medium supplied through the conduit 24 is held at a predetermined constant pressure. The cylinder 25 of the valve has a pressure inlet port 21 and outlet ports 28 and 29 connected by conduits 30 and 3|, respectively, with a return pipe 32 leading back to the reservoir 2|. Reciprocably mounted in the cylinder 25 of the valve structure is a tandem valve unit having valve elements 33 and 34 mounted on a reciprocable rod 35. The left end portion of the rod 35 projects externally of the valve casing, as illustrated in Fig. 2. The valve mechanism is provided with an outlet port 36 which communicates with the right end of an actuating cylinder 31 in which a piston 38 is reciprocably' mounted. The cylinder 31 is stationarily mounted, as illustrated in Fig. l, with.

respect to the base structure of the machine. The piston 38 has a piston rod 39 which is secured to a bracket 40 mounted on the fixture H and through which the fixture II is drlvingly reciprocated to move the drill l4 throughout the foregoing cycle. A passage 4| leading from the left end-of the cylinder 31 communicates with a port 42 leading to the cylinder 25 of the valve mechanism as illustrated in Fig.2. The valve mechanism includes a bleed orifice 43 which is variable by a need1evalve'44 and which forms a communicative connection between the passage 4| and-the left endof the cylinder 25 of the valve mechanism.

The valve mechanism is automatically actuated to the base structure of the machine. The bell crank lever 45 has a downwardly extending arm provided on its lower'extremity with a knob 48 which-is engaged between set screws" carried by fingers 50 andf5l extending downwardly' from the valve actuating rod 35, as viewed in Fig. 2. When the valve mechanism is disposed in the position illustrated in Fig. 2, the pressure supply passage 24 is in direct communication with the port 36 and the passage 4| is in direct communication with the return pipe 32 through the interior of the cylinder 25. This is the condition of the valve mechanism at the-start of a drill operation or afterany one of the successive stages of a drill cycle. Pressure applied on the right end of the cylinder 31 rapidly urges the drill toward the work and as the drill moves toward the work, the lever '45isrotated in a clockwise direction, as viewed in Fig; 2, in timed' relationship to the movement of the drill by mechanism hereinafter described. This rotation of thebell crank 45 causes the valve elements 33 and 34 to be moved in obstructing relationship withrespect to the ports 42 and 36 respectively, thereby decreasing the: rate of flow of fluid to the right endof the cylinder 31- and accordingly reducing the rate of movement of the drill toward the work to a rate which is suitable for the drilling of thematerialof the work. After the drill has performed a predetermined increment of the desired total drilling operatiornfurther clockwise rotation of the bell crank 45 pro"- duced in a manner hereinafter set forth moves tion, the'fluid pressure supply conduit 24 is directly connected with the passage 4| and port 42 in order to rapidly supply fluid medium to the left end portion of the cylinder 31 and to rapidly return the piston 36 to the right end of the cylinder 31, thereby withdrawing the drill away from the work. During this rightward movement of the piston 38 the fluid in the right end portion of the cylinder 31 is permitted to exhaust through the passage 36, left end portion of the cylinder 25 and through the pipe 3| to the return pipe 32. The foregoing cycle is repeated, it being understood that each stage of the cycle involves an increase in the fast portion of the leftward stroke of the piston which is produced by mechanism hereinafter described. Movement of the bell crank lever 45 in timed relationship with respect to the action of the drill is produced by mechanism illustrated mainly in Figs. 4 to 8, inclusive. This mechanism which is also shown in part in Fig. 1 includes a base block 52 which is carried by the bracket 40 and movable in unison with the fixture. H and drill I4. The base block 52 has fixed thereto a plate 53 having teeth 54 along its lower edge. Provided in the lower end portion of the base block 52 is a longitudinally extending channel 55 in which is shiftably mounted a rack bar 56 having teeth 51 on its upper edge disposed in opposed relationship with respect to the teeth 54 of the plate 53. -The rack bar 56 is normally yieldably urged leftwardly, as viewed in Fig. 4, by a spring 58' acting between adjustable nut 59 threaded on a link 60 and an abutment 6| disposedin the channel 55, the link 60 being pivotally attached at 62 to the left end portion of the rack bar. Rightward movement of the rack bar 56 may be variably limited by an adjusting stop screw 63. Leftward movement of the bar 56 by the spring 58 is yieldably opposed by a spring 60' which allows yielding of the bar 56 leftwardly to facilitate placement of the projection 61 between the teeth of the bar 56 and prevents wedging of the teeth in end-to-end relationship.

Slidably mounted in a longitudinally extending recess 64 formed in the left side face of the base block 52, as viewed in Fig. 3, is a stop carriage 65 on which is pivotally mounted a pawl 66 hav ing a lower wedge-shaped projection 61 onit's and fitin the space between the teeth 54 of the plate 53. A coil spring 12 normally yieldably urges the small pawl 10 in a counterclockwise direction, as viewed in Fig. 6, to retain the wedgeshaped projection 1| thereof engaged with the teeth 54.

In Fig. 4 of the drawings, the stop carriage 65 may be consideredas being located in the position thereof corresponding to the commencement of a drillingoperation. .As the base block 52 moves leftwardly, as viewed in-Fig. 2, in unison with the approaching movement of the drill I4 with respect to the work, a roller 13 on the outer extremity of the upper arm of the bell crank lever 45 rides upon the inclined seat 69 of the Y in the teeth of the plate 53 atia'new'location thereon and to disengage the projection 1110i} the" large pawl-86 from the teeth of the rack bar 2,190,234 t A d tremity ot'the base mocr ti eng ges and rotates block to produce the above mentioned" initial clockwise movement oi the bellcrank l5 andleitward movement of the valve-lementsyiland 3}. Further movement of vthe base block not the control apparatus in unison withjtlie drill {I41 brings the roller'13 into engagement with the cam face 68 of the large pawl 56; thereby ro-v tilting" e pawl 66 in a clockwise direction; as

viewed in Fig. 6, to bringits 'wedge-shaped'projection 61 into engagement with the" teeth 5'! 'of the rack bar 56. Quring'thls-cloekwise rota tlonj'ofthe pawl "66 a'pin 'il fixe'd'on the pawl 66 engages a stop screw 15 threaded in the small pawl 10, thereby rotatingthe' latter pawl in' aclockwise direction, as viewedin'fig. 6, to disen gage itswedge-shaped projection j'll fromthe teeth 5101' the plate 53. Y I

'At this stage, the drill I4 is jusflbe'ginnihg to operate upon the work. During the drilling opl eration, the drill advances slowlyinto' the work and the base block 52 continues to move in 'unison therewith at a new rate. Duringthis slow rate movement of the backblock '52, theprojeca tion BT-of the large pawl 66 is held in e l agee ment with the teeth 51 andthestop carriage is held against movement inunison with thebase block by the roller 13 of the bell crank lever.

The large pawl therefore holds the: rack bar 56 against movement in'unison with the block 52,,

thus producing relative movement of; the" latter and the bar 56 of art amountpredetermined-by the set screw 63 which corresponds to the depth :of each increment of drilling;- This action-pro- Jduces a predetermined rightwardshifting oi the stopcarrlage fitl with respect to the fbase'block- 52 and the toothedplate 53; "After this stage {of the operation, the pawlsar'e so ope ated asf'to reengagef the projection II of the small pawl- 10 56, thereby permitting thespring 58" to return the bar 56 to its initial position. i

' The foregoing resetting of the pawlsti and ill is produced by the action of an over'center spring,

device generally designated by the numeral 16 l upon" the bell crank which when the bell crank reaches a predetermined position," produces a snap overaction and rotates theroller 13 of i so" the bell crank in a'clockwise direction out of engagement with the cam 'face 68 of the large pawl lifi. -'I'heover-center spring-1 device isv brought into operation by 'a slight mere e'nt 'of' r movement'ofthe'leverli produced"by'the cam 55 face 68 of the pawl GB-WhenrightWard movement of the bar 56 is arrested by master: screw 63if The movement of thebell-crank 45' by the overcenter: spring device 18 translates the "valveele-j ments as and u to thelr extremeF dotted line" ieftward positions shown in Fig! 2. mm valve mechanism is then set to"applyfluld pressure on the left "side oi' the piston 38 in order'to rapidly return thelatter to the rightend of the cylinder 31 9spreviouslydescribedmf "At thisstag'e ofthe operation, the drill has been rapidly moved "toward the "work, slowly moved into the work for a ShOIUHIStBJlCG and then rapidly withdrawn andrmovedyiroin thei work. "The next step or the cycle comprises a rapid return 10! the drill' towa'rd the work throughout a distance equal to the distance of the first rapid' movement plus theflrst' drilled increment. "At the end of the return stroke of thepistonand drill, a trigger I1 plvotally mount-q edf'at "lfl'ina slo't 'il formed thelower e X-" with the finger! v p therebymoving the latter to itsrightward limit whic earl sition shown :in F1355; ther a lever having a stop ll thereoir which injt engages a pl ger 82 beta valve generally des 87 cluded in a fluid pressure circuit compris duits u anus-by winch mun memum under pressure is" supplied to the leftfend' ot a ylinder "shown inzFig. 2 m" which is' slidably mounted opposed starting and stopping pistons 81 n respectivelw The pistonsyBlandJl mallyf yieldablyurged apart by "a spring F89.

Whenf the fvalve anso emnmd pressure is sup pliedto th'e left endof the cylinder "lilan'dth r starting piston 81 is'urged rightwardly to erase:

1 of h valve control rod 3 ing position a and" simultaneously rotating the bell crank lever in a counterclockwise direction to its initial 'position. Themovement oritne may be I stopped at" any time during the] cycle .0 operationb adjusting a manual control valve the right *end of the cylinder H paratus 'arein the s sition as they were in at the com'mencem the first step of the drilling operatiohex v stop icarriag ,65 which has been advanced thereafter is repeated in the foregoing cycl after 'abore'h'as been drilled to a ancl' it is-=des1red to commence'drilling' veiling stop carriage can be re p p to its original position automaticallyQby eng ment of a sitop 92fiked on thebase block 521 p a lever 33 pivotally mounted on a pin I tionarilyjmouhted withrespectto thebase s ture in or the machine: The stop 92 e gage lever 93i kwhen the drill llhas fdrilledi into e work a desired depth-"and rotates the lever? 93; in af clockwise direction, as viewed in Fig. 5, il i it comes into alignment with a lug 96 on th rightsidei of the stop carriage 65, as viewed 7; The lever: 93' acting through the lug" holds the carriage 65 against movement in t l with the' base block SZpthereby causing" theybas block to move relativeito' the stop carria e unti the latter zhasubeen-repositioned in its 1 position illustrated in Figg ir When' thesto e G5 has reached its initial starting erto its1fulliinepo' yre mi stop carriage to go through thefcycle of t 0 tionsabove' described during the ne complete drilling operation. At the timethe rampl'face engages thepin 89, an abutment I00 carrie the stop carriageilii engages a j'pin 'i-OI ve rt the latterdownwardiy. The lower end of the NH abuts against the trigger I1 and turn ,in a clockwise direction as viewed in Fig i move it out of engagementwith: the valv atinglever 80, thereby permitting the trig pass thelever without actuating it. Movement] of thebaseblock '52 "beyond the position ther The wave a l cam face J02 carried by the base block, with the roller 13 of the bell crank 45. The cam face I02 is so constructed and arranged Iasto return the bell crank lever to a position in which it holds ,the valve elements 33 and 34 inclosing relation with respect to'the ports 42 and 36 thus completely: stopping reciprocating operation of the. drill which may be continuously drivingly rotated if desired. 7 g L I fThe valve mechanism may be started in opera-. tion by manually positioning the valve 90 toadmit fluid under pressurethrough the conduit I04 which leads to the left end of the cylinder 8| and urges the starting piston 8'! rightwardly to engage the finger 5| and thereby return the valves 33 and 34 to their full line starting position shown in Fig. 2. I

Emergency stopping of the apparatus may be accomplished by so setting thevalve 90 as to adi leftwardly against, the finger 5l. While this act-ion takesplace, fluid medium under pressure is I also supplied througha branch conduit l05 to a without mit fluid under pressure to flow therefrom through the conduit 9| to the right end of the cylinder 88 so as to move. the stopping piston 88 cylinder I06 in which is re'ciprocably'mounted a pistonlll'l. The piston I01 has a-piston rod I08 pivotally attached to a lever l 09 which is adapted to. engage a lever IID that is normally urged in a counterclockwise directionfby a [spring ,lll. Counterclockwise rotation of the lever l09 causes clockwiserotation of the lever H0 and-the latter lever has an extension I l 2, which, upon clockwise rot ation,is adapted to lift the trigger l l out of engagement with the lever 80, thereby; permitting thebase block 52, and the drill to return to its fully retracted position without resettingthe valve mechanism to commence a cycle. The

block.65 however, s not reset in position so that the'drill will rapidly return to an operative drilling position when the apparatus-is again started. f Although but one specific embodiment of the invention is herein shown and described,--it will be understood that various changesxin'the size, shape and arrangement of parts may 'bemade tion.

Iclaim; 1.. o 1. In a drill press comprising a fluid pressure system for advancing adrill toward and retracting the same from a piece of workincluding variable-valve mechanism; control apparatus for said valve mechanism including a block movable inv unison with said drill and having a series'cf fixed stops thereon, a bar shiftably mounted on said block havinga series of stops movable-therewith,

a carriageshiftably mounted on said block:hav-' ing a pairof pawls, one engageable with said fixed series of stopsandthe other engageable I with said; movable series of stops, resilient means 1 normally-holding one of said pawls in engagement with said fixedstops forcausing movement oi said carriage and block in unison during initial movement of said. drill toward a piece of work,

means including a member responsive. to move-' ment of .said carriage and engageable with said,

latter pawl fondisengaging the same from said fixed stops and engaging theother pawl with ting during said drilling step, and means responsive to drilling; movement during the final departing from the spirit of the inven "with said fixed stops at a new position and for settingsaid valve mechanism to return said drill and block to their initial positions for performing anothersimilar cycle. s

2. In a drill press comprising a fluid pressure system for advancing a drill toward and retracting-the same from a piece of work including variable valve mechanism; control apparatus for said valve mechanism including a block movable in unisonwithsaid drill andhaving a series of fixed stops thereon, a-bar shiftably mounted on said block having a seriesof stops movable therewith, means for yieldably opposing movement of said bar in opposite directions, a carriage shiftably mounted on said block having a pair of pawls, one engageable with said fixed seriesof stops and the other engageable with said movable series of stops, resilient means normally holding one of said pawlsin engagement with said fixed stops for causing movement of said carriage and block in unison during initialmovement of said drill toward a piece of work, and means including a member responsive to movement of said carriage and engageable with said latter pawl for disengaging the same from said fixed stops and engaging the other pawl with said movable stops to accommodate resetting .movement of said carriage relative to said block during drilling of said work. v

3 In a drill press comprising a fluid pressure system for advancing a drill toward and retracting the same from a piece of work including variable valve mechanism; control apparatus for said valve mechanism including a block movable in unison with said drill and having a series of fixed stops thereon, a bar shiftably mounted on said block having a seriesof stops movable therewith, a carriage shiftably mounted on said block haying apair oi pawls, one engageable with said fixedseries of stops and-the :other engageable.

with said movable series of stops, resilient means normally holding one of said pawls in engagement with said fixed stops for causing movement ing drilling of said-work,'saidmember being operativelyconnected with and adap'tedto maintain said valve mechanism in a drilling speed setting during said drillingstep, means for limitingmovement of said bar relative tolsaid block to predetermine the depth'of each drilling step, said member being'adapted to move slightly relative'to saidcarriagewhen said bar is arrested by said limiting means, and means responsive to said latter movement ofsaid member for moving said member out ofengagement with said carriageto accommodate re-engagement of one of said pawls with said flxed stops at a new position and for setting. said valvemechanism to return said drill and block to their initial posi-.

tions forperforming another similar cycle.

4. Ina drill press comprising, a fluid pressure system Ioradvancing a drill toward and retract-.

ing the same from a piece of work including variable valve mechanism; control apparatus for said valve mechanism including a block movable in unison with said drill and having a series of fixed stops thereon, a barshiitably mounted on said block having a series of stops movable therewith, a carriage shiftably mounted on said block having a pair of pawls, one engageable with said fixed series of stops and the other engageable with said movable series ofstops, resilient means normally holding one of said pawls in engagement with said fixed stops for causing movement of said carriage and block in unison during initial movement of said drill toward a, piece of work,

means including a member responsive to move-- ment of said carriage and engageable with said latter pawl for disengaging the same from said fixed stops and engaging the other pawl with said movable stops to accommodate resetting movement of said carriage relative to said block during drilling 01' said work, said member being operatively connected with and adapted to maintain said valve mechanism in a drilling speed setting during said drilling step, means for limiting movement of saidbar relative to said block to predetermine the depth of each drillingstep, said member being adapted to move slightly relative to said carriage when said bar is arrested by said limiting means, and means responsive to said latter'movement of said member for moving said member out of engagement with said carriage to accommodate re-enga'gement of one, of said pawls with said fixed stops at a new position and for setting said valve mechanism to return saiddrill and block to their initial positions for perof drilling performed forming another similar cycley said limiting means being adjustable and constituting the only essential adjustment required to vary the depth duringeach cycle of a drill ing operation. I

5. In valve operating mechanism comprising a valve setting lever; mechanism for actuating said lever comprising a shiftable block having a series of fixed stops thereon, a bar shiftably mounted on said block having a series of stops movable therewith, resilient means for yieldably opposing movement of said bar relative to said block in respectively opposite directions, a carriage'shiftably mounted on said block having a cam surface engageablewith said lever for actuating the same,,pawl mechanism on said carriage engageable by said lever and having projections alternatively engageable with said fixed and movable stops respectively, resilient means normally holdingone of said projections in engagetion from said fixed stops and engaging the other projection with said movable stops to cause movement of said carriageandbar relative to said block, and meanslfor moving said lever out of' engagementwith said pawl mechanism to release the latter and reset it at a new position with respect to said series of fixed stops. a

8. In valve operating mechanism comprising ing said resilient member and adaptedto acy a valve setting lever; mechanism for actuating said lever comprising a shiitable block a series of fixed stops-thereon, a barshiitably f mounted on said blockhaving a series of stops movable therewith, means for resiliently and y yieldably opposing movement =01 said barrelstive to said block in opposite pdirectionsflin the: course ,of shifting movement of said bloclga car riage shiftably mounted on said block havinga cam surface engageable with said lever for actuating the same, pawl mechanism on said (am riage engageable by said lever and having p'rojec ,tions alternatively engageable with said fixed and movable stops respectively, resilient means not mally holding one of said projections in engagement with said fixed stops to cause movement" of said carriage and block in unison, said pawl, mechanismbeing-movable byengagement theree of with said leverfor releasing the latter projection fromsaid, fixed stops and engagingthe v 3 other projectionwith said movable stops to cause movementof saidcarriage and bar relative to said block, an adjustable limit member for post-H j, tively arresting movement of said bar relative to said block in one direction, and means operables when movement of saidbar isarrestedbyisaidfl limit stop formovingsaid lever out of engagement with said pawl mechanism to release the latter and reset it at a new, position withrespect f, tosaid seriesof fixed stops.

'7. In valve operating mechanism comprisingja valve setting lever; mechanism ioractuating said lever comprising a shiftable block having a series oi fixed stops thereon, a barshittably mounted, on said block having a series oi stops movable I therewith, a carriage shiftably mounted on said block having a cam surface engageable with said lever for actuating the same, pawl mechanism on i said carriage engageable bysaid leverand hav- I ing projections. alternatively engageable withsaid fixed and movable stops respectlvely resilient means normally holdingone; of said projections in engagement with said, fixed stops to cause movement oi 'said carriageand block in unison, said pawl mechanism being movable by engage ment thereotwith, said lever for releasing-the latter projection from said fixed stops and engaging the other projection with said movable 1 stops to cause movementoi said e'arfi'age and bar relative to said block, an adjustable limit memher for arresting movement of said bar relative I to said block,,a resilient member normallyurg ing said bar away from said adjustable limit member, a resilient abutment yleldably oppose.

commodate slight movement of saidsbar away from said adjustable limit member to facilitate engagement of said movable stops and said pawl mechanism, and means for moving said lever out of engagement with said pawl mechanism to release the latter and reset it at a new position with respect to said series of fixed r 

